Positive active material composition for rechargeable lithium battery, positive electrode prepared from composition, and rechargeable lithium battery including positive electrode

ABSTRACT

In an aspect, a positive active material composition for a rechargeable lithium battery including a positive active material coated with a vanadium pentaoxide (V 2 O 5 ) and an aqueous binder, a positive electrode including the same, and a rechargeable lithium battery including the positive electrode is disclosed.

INCORPORATION BY REFERENCE TO RELATED APPLICATIONS

Any and all priority claims identified in the Application Data Sheet, orany correction thereto, are hereby incorporated by reference under 37CFR 1.57. For example, this application is a continuation of U.S. patentapplication Ser. No. 13/888,175 filed May 6, 2013, which claims priorityto and the benefit of Korean Patent Application No. 10-2013-0001271filed on Jan. 4, 2013 in the Korean Intellectual Property Office, thedisclosures of which are incorporated by reference in their entiretiesherein for all purposes.

BACKGROUND

1. Field

This disclosure relates to a positive active material composition for arechargeable lithium battery, a positive electrode obtained therefrom,and a rechargeable lithium battery including the same are disclosed.

2. Description of the Related Technology

A rechargeable lithium battery includes positive and negative electrodesand an organic electrolyte solution or a polymer electrolyte positionedbetween the positive and negative electrodes. Herein, the positive andnegative electrodes intercalate and deintercalate lithium ions andproduce electrical energy through oxidation and reduction reactions.

As for a positive active material for a lithium rechargeable battery, anoxide that has a structure of intercalating and deintercalating lithiumions and includes lithium and a transition element, for example, alithium cobalt oxide (LiCoO₂), a lithium nickel oxide (LiNiO₂), or alithium nickel cobalt manganese oxide (Li[NiCoMn]O₂,Li[Ni_(1-x-y)Co_(x)M_(y)]O₂), and the like, have been investigated.

When the positive active material for a rechargeable lithium battery isused with an aqueous binder to fabricate a positive electrode, thepositive active material provides unreacted alkali metal ionsdissociated into water, which dramatically increases the pH of thepositive active material slurry and makes the positive active materialslurry strongly basic.

Accordingly, when such an aqueous positive active material slurry havingstrong basicity is coated on a metal current collector, the metalcurrent collector may be corroded due to the high pH of the material andgenerate H₂ gas and thus, make numerous pinholes on the positiveelectrode and increase internal resistance of the positive electrode.

In order to solve this problem, Japanese Patent No. 4114247 (2008 Apr.25) discloses a non-aqueous electrolyte rechargeable battery including amolybdenum trioxide (MoO₃) component in a positive electrode. However,the molybdenum trioxide (MoO₃) has low electrical conductivity and thus,may increase resistance of an electrode and deteriorate charge anddischarge characteristics of the lithium rechargeable battery.

In addition, Japanese Patent Laid-Open Publication No. 2010-021027 (2010Jan. 28) discloses a method of coating various metal oxides on an A1current collector. However, the method needs additional processing andthus, increases a cost due to the additional processing.

Accordingly, additional research on a novel aqueous positive activematerial composition to prevent corrosion of a metal current collectoris needed.

SUMMARY

One embodiment provides a positive active material composition for arechargeable lithium battery that prevents corrosion of a metal currentcollector and has high electrical conductivity.

Another embodiment provides a positive electrode for a rechargeablelithium battery that decreases resistance of an electrode and ensuresexcellent high rate capability and cycle-life characteristics.

Still another embodiment provides a rechargeable lithium batteryincluding the same.

Some embodiments provide a method of preparing a positive activematerial that includes mixing a positive active material, a vanadiumpentaoxide (V₂O₅), and an organic solvent, agitating the mixture toevaporate the organic solvent, and then, heating the resultant mixtureto prepare a positive active material coated with the vanadiumpentaoxide.

In some embodiments, the positive active material may include at leastone selected from a lithium cobalt-based oxide, a lithium nickel cobaltmanganese-based oxide, and a lithium nickel cobalt aluminum-based oxide.In some embodiments, the lithium cobalt-based oxide may beLi_(a)A_(1-b)R_(b)D¹ ₂ where A is Co and D¹ is O (oxygen) (0.90≦a≦1.8and 0≦b≦0.5). In some embodiments, the lithium nickel cobaltmanganese-based oxide may be Li_(a)Ni_(1-b-c)Co_(b)R_(c)D¹ _(α), where Ris Co and D¹ is O (oxygen) (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and 0<α≦2). Insome embodiments, the Li_(a)Ni_(1-b-c)Co_(b)R_(c)D¹ _(α), may beLi[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂. In some embodiments, the lithium nickelcobalt aluminum-based oxide may be Li_(a)Ni_(1-b-c)Co_(b)R_(c)D¹ _(α),where R is Al and D¹ is O (oxygen) (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and0<α≦2).

In some embodiments, the vanadium pentaoxide (V₂O₅) may be included inan amount of about 0.1 parts to about 5 parts by weight based on 100parts by weight of the positive active material.

In some embodiments, the organic solvent may be a carbonate-based,alcohol-based, ester-based, ether-based, ketone-based, or aromatichydrocarbon-based solvent, an aprotic solvent, or a combination thereof.

In some embodiments, the heating may be performed at about 620° C. toabout 730° C.

Some embodiments provide a positive active material composition for arechargeable lithium battery that includes the positive active materialcoated with the vanadium pentaoxide (V₂O₅) and an aqueous binder.

In some embodiments, the vanadium pentaoxide (V₂O₅) may be coated on thesurface of the positive active material into an island shape.

In some embodiments, the vanadium pentaoxide (V₂O₅) may be included inan amount of about 0.1 parts to about 5 parts by weight based on 100parts by weight of the positive active material.

In some embodiments, the vanadium pentaoxide (V₂O₅) may be included inan amount of about 0.1 parts to about 1 part by weight based on 100parts by weight of the positive active material.

In some embodiments, the positive active material coated with thevanadium pentaoxide may be prepared according to the preparing methoddescribed above.

In some embodiments, the positive active material may include at leastone selected from a lithium cobalt-based oxide, a lithium nickel cobaltmanganese-based oxide, and a lithium nickel cobalt aluminum-based oxide.In some embodiments, the lithium cobalt-based oxide may beLi_(a)A_(1-b)R_(b)D¹ ₂ where A is Co and D¹ is O (oxygen) (0.90≦a≦1.8and 0≦b≦0.5). In some embodiments, the lithium nickel cobaltmanganese-based oxide may be Li_(a)Ni_(1-b-c)Co_(b)R_(c)D¹ _(α) where Ris Mn and D¹ is O (oxygen) (0.90≦a≦1.8, 0≦b≦0.5, 0<c≦0.05 and 0<α≦2). Insome embodiments, the Li_(a)Ni_(1-b-c)Co_(b)R_(c)D¹ _(α) may beLi[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂. In some embodiments, the lithium nickelcobalt aluminum-based oxide may be Li_(a)Ni_(1-b-c)Co_(b)R_(c)D¹ _(α)where R is A1 and D¹ is O (oxygen) (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and0<α≦2).

In some embodiments, the aqueous binder may include at least oneselected from carboxylmethylcellulose, hydroxyethylcellulose,hydroxypropylcellulose, hydroxypropylmethylcellulose, polyvinylidenefluoride, polytetrafluoroethylene, polyethylene, polypropylene,polybutadiene, polyethyleneoxide, polyvinylalcohol, polyacrylic acid anda salt thereof, polyvinylpyrrolidone, polyepichlorohydrine,polyphosphazene, polyacrylonitrile, polystyrene, polyvinylpyridine,chlorosulfonated polyethylene, a polyester resin, an acrylic resin, aphenolic resin, an epoxy resin, a polymer of propylene and C2 to C8olefin, a copolymer of (meth)acrylic acid and (meth)acrylic acidalkylester, acryl-based copolymer emulsion, and a combination thereof.

In some embodiments, the aqueous binder may be included in an amount ofabout 0.1 parts to about 10 parts by weight based on 100 parts by weightof the positive active material.

In some embodiments, the positive active material composition for arechargeable lithium battery may further include a conductive material.

In some embodiments, the conductive material may include at least oneselected from natural graphite, artificial graphite, carbon black,acetylene black, ketjen black, a carbon fiber, carbon nanotube, a metalpowder, a metal fiber, and a conductive polymer.

Some embodiments provide a positive electrode for a rechargeable lithiumbattery that includes a metal current collector having corrodibility instrong alkali media; and the positive active material layer disposed byusing the positive active material composition on at least one surfaceof the metal substrate.

In some embodiments, the metal current collector may be an aluminumsubstrate.

Some embodiments provide a rechargeable lithium battery including thepositive electrode; a negative electrode including a negative activematerial; a separator interposed between the positive and negativeelectrodes; and an electrolyte.

In some embodiments, the positive active material composition preventscorrosion of the metal current collector in a rechargeable lithiumbattery and simultaneously has high electrical conductivity. In someembodiments, the positive active material composition decreasesresistance of the electrode and ensures excellent high rate capabilityand cycle-life characteristic of the rechargeable lithium battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a rechargeable lithium batteryaccording to one embodiment.

FIG. 2 shows the X-ray diffraction (XRD) pattern of a positive activematerial according to Preparation Example 1.

FIG. 3 shows the X-ray diffraction (XRD) pattern of a positive activematerial according to Comparative Preparation Example 1.

FIG. 4 is a scanning electron microscope showing the surface of thepositive electrode according to one embodiment.

FIG. 5 is a scanning electron microscope showing the surface of thepositive electrode according to Comparative Example.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure will hereinafter bedescribed in detail. However, these embodiments are only exemplary, andthis disclosure is not limited thereto.

Some embodiments provide a positive active material composition for arechargeable lithium battery including a positive active material coatedwith vanadium pentaoxide (V₂O₅) and an aqueous binder.

In some embodiments, the vanadium pentaoxide (V₂O₅) may be coated on thesurface of the positive active material into an island shape.

In some embodiments, the positive active material composition may be anaqueous positive active material composition capable of using water as asolvent.

Typically, a positive electrode for a rechargeable lithium batteryincludes an aluminum substrate playing a role of a current collector anda thin aluminum oxide (Al₂O₃) film on the surface thereof. This aluminumoxide film may hinder reaction between an aluminum metal and water in aneutral aqueous solution and suppress generation of hydrogen gasaccording to the following Reaction Scheme 1.

2Al+3H₂O→Al₂O₃+3H₂↑  (Reaction Scheme 1)

However, aluminum oxide (Al₂O₃) reacts according to the followingReaction Scheme 2 in an alkali aqueous solution and provides analuminate ion (AlO₂ ⁻) into the solution and thus, exposes aluminummetal on the surface of the current collector allowing another reactionaccording to the following Reaction Scheme 3. Herein, the reactiongenerates hydrogen gas, which forms a pin hole on the surface of anelectrode.

Al₂O₃+H₂O+2OH⁻→2AlO₂ ⁻+2H₂O   (Reaction Scheme 2)

2Al+6OH⁻+6H₂O→2[Al(OH)₆]³⁻+3H₂↑  (Reaction Scheme 3)

In contrast, a positive active material coated with a vanadiumpentaoxide (V₂O₅) may suppress the reaction according to the ReactionScheme 3 under basic conditions but cause formation of an aluminum oxidefilm according to the following Reaction Scheme 4, since the vanadiumpentaoxide (V₂O₅) is a strong oxidant.

2Al+3V₂O₅→Al₂O₃+3V₂O₄   (Reaction Scheme 4)

In some embodiments, the vanadium pentaoxide (V₂O₅) prevents corrosionof aluminum, suppresses formation of pin holes on an electrode and thus,may suppress increase of electrode resistance.

In addition, the vanadium pentaoxide (V₂O₅) has low electricalresistivity of about 197 nωm and provides the positive active materialwith high electrical conductivity and thus, may decrease resistance ofthe electrode and secure excellent high rate capability and cycle-lifecharacteristics of a rechargeable lithium battery.

In some embodiments, the positive active material coated with thevanadium pentaoxide may be prepared by mixing a positive activematerial, vanadium pentaoxide (V₂O₅) and an organic solvent, removingthe organic solvent and heating the resultant mixture after removal ofthe organic solvent. In some embodiments, the removal of the organicsolvent may be accomplished by agitation of the mixture to evaporate theorganic solvent.

In some embodiments, the organic solvent may be highly volatile.Examples of the organic solvent may include a carbonate-based,alcohol-based, ester-based, ether-based, ketone-based, or aromatichydrocarbon-based solvent, an aprotic solvent, or a combination thereof.

In some embodiments, the organic solvent may include methanol, ethanol,n-propanol, isopropanol, n-butanol, t-butylalcohol, ethylene glycoldimethacrylate, methylethylketone (butanone), methylisobutylketone,benzene, toluene, ethylene carbonate, dimethyl carbonate, ethylmethylcarbonate, N-methyl pyrrolidone, or a combination thereof, but is notlimited thereto.

In some embodiments, the agitation of the mixture to evaporate theorganic solvent may be performed at about 30° C. to about 90° C. andspecifically, about 30° C. to about 70° C. or about 30° C. to about 50°C.

In some embodiments, the resultant mixture after evaporating the organicsolvent may be heated in the range of from about 620° C. to about 730°C. When the heating is performed within the temperature range of fromabout 620° C. to about 730° C., the vanadium pentaoxide (V₂O₅) may notbe decomposed but appropriately attached to the surface of the positiveactive material in an island shape. Since vanadium pentaoxide (V₂O₅) hasa melting point ranging from about 650° C. to about 700° C., thevanadium pentaoxide (V₂O₅) may not bond with the positive activematerial but be detached therefrom when the calcinating is performed ata temperature of less than about 620° C. On the contrary, when thecalcinating is performed at a temperature of higher than about 730° C.,the vanadium pentaoxide (V₂O₅) is doped inside the positive activematerial and may have no effect on suppressing corrosion of the currentcollector.

The amount of the vanadium pentaoxide (V₂O₅) is included in the positiveactive material with no particular limit. However, when vanadiumpentaoxide (V₂O₅) is included in an excessively small amount, corrosionof an aluminum current collector may not be effectively prevented, whilewhen vanadium pentaoxide (V₂O₅) is included in an excessively largeamount, the positive active material may be included in a relativelysmall amount in an electrode, decreasing capacity. In addition, when thevanadium pentaoxide (V₂O₅) is included in greater quantity than theactive material, the active material may deteriorate density per unitcapacity all over the electrode.

In some embodiments, the vanadium pentaoxide (V₂O₅) may be included inan amount of about 0.1 parts to about 5 parts by weight, specificallyabout 0.1 parts to about 4 parts by weight, about 0.1 parts to about 3parts by weight, about 0.1 parts to about 2 parts by weight, about 0.1parts to about 1 parts by weight based on 100 parts by weight of thepositive active material.

In some embodiments, the positive active material may be any positiveactive material in this art, unless the positive active material is weakfor an aqueous binder and an aqueous solvent and elutes a metal ion.

For example, a lithiated intercalation compound that may reversiblyintercalate and deintercalate lithium ions may be used. Examples thereofmay be a composite oxide of lithium and a metal selected from cobalt,manganese, nickel, and a combination thereof. Examples of the positiveactive material are compounds represented by the following chemicalformulae:

-   Li_(a)A_(1-b)R_(b)D¹ ₂ (0.90≦a≦1.8 and 0≦b≦0.5);-   Li_(a)E_(1-b)R_(b)O_(2-c)D¹ _(c) (0.90≦a≦1.8, 0≦b≦0.5 and 0≦c≦0.05);-   LiE_(2-b)R_(b)O_(4-c)D¹ _(c) (0≦b≦0.5, 0≦c≦0.05);-   Li_(a)Ni_(1-b-c)Co_(b)R_(c)D¹ _(α) (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05    and 0<α≦2);-   Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2−α)Z_(α) (0.90≦a≦1.8, 0≦b≦0.5,    0≦c≦0.05 and 0<α≦2);-   Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2−α)Z₂ (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05    and 0<α≦2);-   Li_(a)Ni_(1-b-c)Mn_(b)R_(c)D¹ _(α) (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05    and 0<α≦2);-   Li_(a)Ni_(1-b-c)Mn_(b)R_(c)O_(2−α)Z_(α) (0.90≦a≦1.8, 0≦b≦0.5,    0≦c≦0.05 and 0<α≦2);-   Li_(a)Ni_(1-b-c)Mn_(b)R_(c)O_(2−α)Z₂ (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05    and 0<α≦2);-   Li_(a)Ni_(b)E_(c)G_(d)O₂ (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5 and    0.001≦d≦0.1.);-   Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂ (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5    and 0.001≦e≦0.1.);-   Li_(a)NiG_(b)O₂ (0.90≦a≦1.8 and 0.001≦b≦0.1.);-   Li_(a)CoG_(b)O₂ (0.90≦a≦1.8 and 0.001≦b≦0.1.);-   Li_(a)MnG_(b)O₂ (0.90≦a≦1.8 and 0.001≦b≦0.1.);-   Li_(a)Mn₂G_(b)O₄ (0.90≦a≦1.8 and 0.001≦b≦0.1.);-   QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅; LiTO₂; LiNiVO₄; Li(_(3-f))J₂(PO₄)₃    (0≦f≦2); Li_((3-f))Fe₂(PO₄)₃ (0≦f≦2); and LiFePO₄.

In the above chemical formulae, A may be Ni, Co, Mn, or a combinationthereof; R may be Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earthelement, or a combination thereof; D¹ may be O (oxygen), F (fluorine), S(sulfur), P (phosphorus), or a combination thereof; E may be Co, Mn, ora combination thereof; Z is F (fluorine), S (sulfur), P (phosphorus), ora combination thereof; G may be Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or acombination thereof; Q may be Ti, Mo, Mn, or a combination thereof; Tmay be Cr, V, Fe, Sc, Y, or a combination thereof; and J may be V, Cr,Mn, Co, Ni, Cu, or a combination thereof.

In some embodiments, the positive active material composition has anaqueous system and thus, includes an aqueous binder using water as asolvent. The aqueous binder plays a role of thoroughly attachingpositive active material particles to one another and the positiveactive material particles to the current collector and also works as athickener of increasing viscosity of the positive active materialcomposition.

The aqueous binder is compatible with moisture and does not need to behandled under anhydrous conditions unlike a non-aqueous binder like NMP(N-methyl-pyrrolidone). The aqueous binder needs no recycling processand thus, is environmentally-friendly and also, decreases manufacturingequipment. In addition, the aqueous binder has a binding mechanismhaving no much influence on the specific surface area of materials usedin the electrode and may be applied to various materials having a largespecific surface area and also, has the low heat generation due to thelow reactivity with an electrolyte and thus, excellent stability.

Examples of the aqueous binder may include carboxylmethylcellulose,hydroxyethylcellulose, hydroxypropylcellulose,hydroxypropylmethylcellulose, polyvinylidene fluoride,polytetrafluoroethylene, polyethylene, polypropylene, polybutadiene,polyethyleneoxide, polyvinylalcohol, polyacrylic acid and a saltthereof, polyvinylpyrrolidone, polyepichlorohydrine, polyphosphazene,polyacrylonitrile, polystyrene, polyvinylpyridine, chlorosulfonatedpolyethylene, a polyester a resin, an acrylic resin, a phenolic resin,an epoxy resin, a polymer of propylene and C2 to C8 olefin, a copolymerof (meth)acrylic acid and (meth)acrylic acid alkylester, and the like,but are not limited thereto. Any aqueous binder in this art may be used.

In some embodiments, the binder may be used singularly or as a mixtureof two or more binders.

In some embodiments, the aqueous binder may be used in an appropriateamount enough to apply a binding force among positive active materialparticles and between the positive active material particles and acurrent collector and viscosity of the positive active materialcomposition without a particular limit. For example, the aqueous bindermay be used in an amount of about 0.1 parts to about 10 parts by weight,specifically, about 1 parts to about 8 parts by weight, and morespecifically, about 4 parts to about 8 parts by weight based on 100parts by weight of the positive active material.

In some embodiments, the positive active material composition for arechargeable lithium battery may further include a conductive material.The conductive material improves electrical conductivity of the negativeelectrode. Any electrically conductive material may be used, unless itcauses a chemical change.

Examples of the conductive material may include at least one selectedfrom natural graphite, artificial graphite, carbon black, acetyleneblack, ketjen black, a carbon fiber, a metal powder or a metal fiberincluding copper, nickel, aluminum, silver, and the like, and the like,or a polyphenylene derivative and the like.

In some embodiments, the conductive material may be included in anamount of about 1 part to about 20 parts by weight based on 100 parts byweight of the positive active material.

Some embodiments provide a positive electrode for a rechargeable lithiumbattery that includes a metal current collector having corrodibility forstrong alkali; and a positive active material layer disposed on at leastone surface of the metal current collector. In some embodiments, thepositive active material layer may be formed by using the positiveactive material composition.

In the positive electrode, the metal current collector includes anymaterial, unless it causes chemical changes but has high conductivity.For example, the metal current collector may be stainless steel,aluminum, nickel, titanium, fired carbon, or aluminum, or stainlesssteel that is surface-treated with carbon, nickel, titanium, silver, andthe like. The metal current collector having corrodibility for strongalkali may include, for example, an aluminum substrate. In someembodiments, the aluminum substrate may be effectively prevented fromcorrosion by applying the positive active material composition thereon.In some embodiments, the metal current collector may have a thicknessranging from 3 μm to 500 μm but is not limited thereto.

In some embodiments, the positive electrode may be fabricated by moldingthe positive active material composition into a predetermined shape orcoating the positive active material composition on the metal currentcollector such as an aluminum foil and the like.

In some embodiments, the positive active material composition may bedirectly coated and dried on the metal current collector to form apositive active material layer. In some embodiments, a positive activematerial layer may be formed by casting the slurry composition on aseparate supporter and peeling off a formed film from the supporter andthen, laminating the film on the metal substrate. In some embodiments,the positive electrode may be fabricated in various ways other than theaforementioned methods to an ordinary skilled person in a related field.

Some embodiments provide a rechargeable lithium battery including thepositive electrode; a negative electrode including a negative activematerial; a separator interposed between the positive and negativeelectrodes; and an electrolyte is provided.

FIG. 1 is a schematic view showing the representative structure of arechargeable lithium battery according to one embodiment. As shown inFIG. 1, the rechargeable lithium battery 1 includes a positive electrode3, a negative electrode 2, and a separator interposed between thepositive electrode 3 and the negative electrode 2, an electrolyteimpregnated therein, a battery case 5 including the foregoing elements,and a sealing member sealing the battery case 5.

In some embodiments, the negative electrode of the rechargeable lithiumbattery includes a current collector and a negative active materiallayer formed on the current collector, and the negative active materiallayer includes a negative active material.

In some embodiments, the negative active material may include a materialthat reversibly intercalates/deintercalates lithium ions, a lithiummetal, a lithium metal alloy, a material being capable ofdoping/dedoping lithium, or a transition metal oxide.

In some embodiments, the material that reversiblyintercalates/deintercalates lithium ions may be a carbon material. Insome embodiments, the carbon material may be any generally-usedcarbon-based negative active material used in a lithium ion rechargeablebattery. Examples of the carbon-based negative active material mayinclude crystalline carbon, amorphous carbon, or a combination thereof.In some embodiments, the crystalline carbon may be non-shaped, or sheet,flake, spherical, or fiber-shaped natural graphite or artificialgraphite. In some embodiments, the amorphous carbon may be a softcarbon, a hard carbon, a mesophase pitch carbonized product, fired coke,and the like.

In some embodiments, the lithium metal alloy may be an alloy of lithiumand a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb,In, Zn, Ba, Ra, Ge, Al, and Sn.

In some embodiments, the material being capable of doping/dedopinglithium may include Si, SiO_(x) (0<x≦2), a Si-C composite, a Si-Q alloy(wherein Q is an alkali metal, an alkaline-earth metal, Group 13 to 16elements, a transition element, a rare earth element, or a combinationthereof, and not Si), Sn, SnO₂, a Sn-C composite, a Sn-R alloy (whereinR is an alkali metal, an alkaline-earth metal, Group 13 to 16 elements,a transition element, a rare earth element, or a combination thereof,and not Sn), and the like. In some embodiments, the elements Q and R maybe selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta,Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu,Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po,or a combination thereof. In some embodiments, the elements Q and R maybe Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Re, Fe, Pb,Ru, Os, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge,P, As, Sb, Bi, S, Se, Te, or a combination thereof.

In some embodiments, the transition metal oxide may include a vanadiumoxide, a lithium vanadium oxide, and the like.

In some embodiments, the negative active material layer includes abinder and optionally, a conductive material.

The binder improves binding properties of the negative active materialparticles to one another and to a current collector. The binder includesa non-water-soluble binder, a water-soluble binder, or a combinationthereof. The non-water-soluble binder includes polyvinylchloride,carboxylated polyvinylchloride, polyvinylfluoride, an ethyleneoxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, polyamideimide, polyimide, or a combination thereof. Thewater-soluble binder includes a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, acopolymer of propylene and a C2 to C8 olefin, a copolymer of(meth)acrylic acid and (meth)acrylic acid alkyl ester, or a combinationthereof. When the water-soluble binder is used as a negative electrodebinder, a cellulose-based compound may be further used to provideviscosity. The cellulose-based compound includes one or more ofcarboxylmethyl cellulose, hydroxypropylmethyl cellulose, methylcellulose, or alkali metal salts thereof. The alkali metal may be Na, K,or Li. The cellulose-based compound may be included in an amount ofabout 0.1 to about 3 parts by weight based on 100 parts by weight of thenegative active material.

The conductive material improves electrical conductivity of the negativeelectrode. Any electrically conductive material can be used as aconductive agent unless it causes a chemical change. Examples of theconductive material include a carbon-based material such as naturalgraphite, artificial graphite, carbon black, acetylene black, ketjenblack, a carbon fiber, and the like; a metal-based material of a metalpowder or a metal fiber including copper, nickel, aluminum, silver, andthe like; a conductive polymer such as a polyphenylene; or a mixturethereof.

In some embodiments, the current collector may be a copper foil, anickel foil, a stainless steel foil, a titanium foil, a nickel foam, acopper foam, a polymer substrate coated with a conductive metal, or acombination thereof.

In some embodiments, the negative electrode may be manufactured in amethod of preparing a negative active material composition by mixing thenegative active material, a conductive material, and a binder andcoating the composition on a current collector. The electrodemanufacturing method is well known and thus, is not described in detailin the present specification. In some embodiments, the solvent includesN-methylpyrrolidone, water and the like but is not limited thereto.

The separator may include any materials commonly used in theconventional lithium battery, as long as separating a negative electrodefrom a positive electrode and providing a transporting passage forlithium ions. In other words, the separator may be made of a materialhaving low resistance to ion transportation and excellent impregnationfor an electrolyte. For example, the material may be selected from glassfiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene(PTFE), or a combination thereof and have a form of a non-woven fabricor a woven fabric. For example, a polyolefin-based polymer separatorsuch as polyethylene, polypropylene or the like is mainly used for alithium ion battery. In order to ensure heat resistance or mechanicalstrength, a coated separator including a ceramic component or a polymermaterial may be used and selectively, have a mono-layered ormulti-layered structure.

In some embodiments, the electrolyte includes a non-aqueous organicsolvent and a lithium salt.

The non-aqueous organic solvent serves as a medium for transmitting ionstaking part in the electrochemical reaction of a battery.

In some embodiments, the non-aqueous organic solvent may be selectedfrom a carbonate-based, ester-based, ether-based, ketone-based,alcohol-based, or aprotic solvent. The carbonate-based solvent mayinclude, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC),dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropylcarbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC),propylene carbonate (PC), butylene carbonate (BC), and the like, and theester-based solvent may include methyl acetate, ethyl acetate, n-propylacetate, 1,1-dimethylethyl acetate, methylpropinonate, ethylpropinonate,γ-butyrolactone, decanolide, valerolactone, mevalonolactone,caprolactone, and the like. In some embodiments, the ether-based solventmay include dibutyl ether, tetraglyme, diglyme, dimethoxyethane,2-methyltetrahydrofuran, tetrahydrofuran, and the like, and theketone-based solvent may include cyclohexanone, and the like. In someembodiments, the alcohol-based solvent may include ethanol,isopropylalcohol, and the like. In some embodiments, the aprotic solventinclude nitriles such as R—CN (wherein R is a C2 to C20 linear,branched, or cyclic hydrocarbon group, and may include one or moredouble bonds, one or more aromatic rings, or one or more ether bonds),amides such as dimethylformamide, dimethylacetamide, dioxolanes such as1,3-dioxolane, sulfolanes, and the like.

In some embodiments, the non-aqueous organic solvent may be usedsingularly or in a mixture. When the organic solvent is used in amixture, the mixture ratio may have a ratio controlled in accordancewith desirable performance of a battery.

In some embodiments, the carbonate-based solvent may include a mixtureof a cyclic carbonate and a linear carbonate. The cyclic carbonate andthe linear carbonate are mixed together in a volume ratio of about 1:1to about 1:9 as an electrolyte, and the electrolyte may have enhancedperformance.

In some embodiments, the non-aqueous organic solvent may be prepared byfurther adding the aromatic hydrocarbon-based solvent to thecarbonate-based solvent.

The carbonate-based solvent and the aromatic hydrocarbon-based solventare mixed together in a volume ratio of about 1:1 to about 30:1.

In some embodiments, the aromatic hydrocarbon-based organic solvent maybe an aromatic hydrocarbon-based compound represented by the followingChemical Formula 1.

wherein in Chemical Formula 1, R₁ to R₆ are independently hydrogen, ahalogen, a C1 to C10 alkyl group, a C1 to C10 haloalkyl group, or acombination thereof.

In some embodiments, the aromatic hydrocarbon-based organic solvent maybe selected from benzene, fluorobenzene, 1,2-difluorobenzene,1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene,1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene,1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene,1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene,1,2,4-triiodobenzene, toluene, fluorotoluene, 1,2-difluorotoluene,1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluorotoluene,1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene,1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene,1,2,4-trichlorotoluene, iodotoluene, 1,2-diiodotoluene,1,3-diiodotoluene, 1,4-diiodotoluene, 1,2,3-triiodotoluene,1,2,4-triiodotoluene, xylene, and a combination thereof.

In some embodiments, the non-aqueous electrolyte may further includevinylene carbonate or an ethylene carbonate-based compound representedby the following Chemical Formula 2 in order to improve cycle-life of abattery.

wherein in Chemical Formula 2, R₇ and R₈ are independently hydrogen, ahalogen, a cyano group (CN), a nitro group (NO₂), or a C1 to C5fluoroalkyl group, provided that at least one of R₇ and R₈ is halogen, acyano group (CN), a nitro group (NO₂), or a C1 to C5 fluoroalkyl group.

Examples of the ethylene carbonate-based compound include difluoroethylenecarbonate, chloroethylene carbonate, dichloroethylene carbonate,bromoethylene carbonate, dibromoethylene carbonate, nitroethylenecarbonate, cyanoethylene carbonate or fluoroethylene carbonate, and thelike. In some embodiments, the use amount of the vinylene carbonate orthe ethylene carbonate-based compound may be adjusted within anappropriate range.

The lithium salt is dissolved in the non-aqueous solvent, supplieslithium ions in a rechargeable lithium battery, and basically operatesthe rechargeable lithium battery and thus, improves lithium ion transferbetween the positive and negative electrodes. In some embodiments, thelithium salt include at least one supporting salt selected from LiPF₆,LiBF₄, LiSbF₆, LiAsF₆, LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x-1)SO₂)(C_(y)F_(2y-1)SO₂) (wherein, x and y are naturalnumbers of 1 to 20, respectively), LiCl, LiI, LiB(C₂O₄)₂ (lithiumbis(oxalato) borate), and a combination thereof. In some embodiments,the lithium salt may be used in a concentration of about 0.1 to about2.0M. When the lithium salt is included within the above concentrationrange, an electrolyte may have excellent performance and lithium ionmobility due to optimal electrolyte conductivity and viscosity.

Hereinafter, the following examples illustrate the present invention inmore detail. These examples, however, should not in any sense beinterpreted as limiting the scope of the present invention.

EXAMPLES Fabrication of Positive electrode Preparation Example 1

10 g of a V₂O₅ solution (concentration: 10 wt %, solvent: water), 200 gof Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂, and 12 g of ethanol were mixed, andthe mixture was agitated at 40° C. to evaporate ethanol. The resultingproduct was heated at a rate of 1° C./min until the temperature reachedto 650° C., heated for 2 hours at this temperature, i.e., 650° C. whilethe temperature was maintained, and cooled down to 300° C. for 5 hoursto coat the Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂ with the V₂O₅, therebypreparing a positive active material. In the resulting positive activematerial, V₂O₅ was coated on the surface of the positive active materialinto an island shape.

100 g of the Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂ coated with the V₂O₅ weremixed with 13.4 g of acetylene black and 3.3 g of carboxylmethylcellulose in 75 g of water. Subsequently, 70 g of water and 25 g (40 wt%) of an acryl-based copolymer emulsion (AX-4069, Japan, Xeon Inc.) wereadditionally added thereto, and the resulting mixture was mixed,preparing a positive active material composition. The positive activematerial composition was coated on an aluminum foil and dried at 100° C.for 10 minutes, fabricating a positive electrode.

Preparation Example 2

A positive electrode was fabricated according to the same method asPreparation Example 1 except for using 5 g (10 wt %) of a V₂O₅ solution.

Preparation Example 3

A positive electrode was fabricated according to the same method asPreparation Example 1 except for using 15 g (10 wt %) of a V₂O₅solution.

Comparative Preparation Example 1

A positive electrode was fabricated according to the same method asPreparation Example 1 except for using Li [Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂that was not coated with V₂O₅.

Fabrication of Rechargeable Lithium Battery Cell (Coin Cell) Example 1

A coin cell (a CR2032 type) having a diameter of 20 mm was fabricatedusing the positive electrode according to Preparation Example 1 and anegative electrode. The negative electrode was fabricated by mixing 97.5g of graphite, 1 g of carboxylmethyl cellulose (CMC), and 50 g of waterand then adding 1.5 g of BM400B as a binder (styrene-butadiene rubber,40% of a solid content, solvent: water) and 50 g of water thereto toprepare a slurry. The slurry was coated on a copper film followed bydrying. A polyethylene/polypropylene separator, and an electrolyte wereused to complete fabrication of the coin cell. The electrolyte wasprepared by mixing ethylene carbonate (EC): diethyl carbonate (DEC):dimethyl carbonate (DMC) 1:1:8 volume ratio and dissolving 1.3 M LiPF₆therein.

Examples 2 and 3

Coin cells were fabricated in the same method as Example 1 byrespectively using the positive electrode according to PreparationExamples 2 and 3.

Comparative Example 1

A coin cell was fabricated in the same method as Example 1 except forusing the positive electrode according to Comparative PreparationExample 1.

Evaluation Example 1 Evaluation of X-ray Diffraction (XRD)

FIG. 2 shows the X-ray diffraction pattern of the positive activematerial according to Preparation Example 1, which includes Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂ coated with V₂O₅. In addition, FIG. 3 showsthe X-ray diffraction pattern of the positive active material accordingto Comparative Preparation Example 1, which is Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂ that is not coated with V₂O₅.

In FIG. 2, a part marked with a circle is a peak showing vanadium (V).Referring to FIGS. 2 and 3, the positive active material according toPreparation Example 1 includes a peak corresponding to vanadium and thepositive active material according to Comparative Preparation Example 1does not include a peak corresponding to vanadium.

Evaluation Example 2 Pin Holes on Surface of Positive Electrode

The positive electrode according to Preparation Examples 1 to 3 andComparative Preparation Example 1 were examined to have pin holes on thesurface generated by hydrogen gas. The result is provided in thefollowing Table 1.

In addition, FIG. 4 shows the scanning electron microscope (SEM) of thepositive electrode according to Preparation Example 1, and FIG. 5 showsthe scanning electron microscope (SEM) of the positive electrodeaccording to Comparative Preparation Example 1.

TABLE 1 H₂ pin holes Preparation Example 1 Not observed PreparationExample 2 Not observed Preparation Example 3 Not observed ComparativePreparation Example 1 Yes

As shown in Table 1, the positive electrode according to ComparativePreparation Example 1 had pin holes, while the positive electrodeaccording to Preparation Examples 1 to 3 had no pin holes.

Referring to FIG. 5, the positive electrode according to ComparativePreparation Example 1 shows pin holes. On the other hand, the positiveelectrode according to Example 1 did not have pin holes as shown in FIG.4.

Evaluation Example 3 Cycle-Life Characteristics

The rechargeable lithium battery cells according to Examples 1 to 3 andComparative Example 1 were charged at 0.8C and discharged at 1.0C within3V to 4.2V for 100 times. The capacity retention (%) was obtained fromthe ratio of the capacity of the 100th cycles relative to the capacityof the first cycle. The results are provided in the following Table 2.

TABLE 2 Capacity retention (%) Example 1 91.2 Example 2 87.9 Example 386.3 Comparative Example 1 73.7

Referring to Table 2, the rechargeable lithium battery cells of Examples1 to 3 had a capacity retention ranging from 86.3 to 91.2% and thus,excellent cycle-life characteristic compared with the rechargeablelithium battery cells of Comparative Example 1.

In the present disclosure, the terms “Example,” “Comparative Example,”“Evaluation Example ” and “Preparation Example” are used arbitrarily tosimply identify a particular example or experimentation and should notbe interpreted as admission of prior art. While the embodiments havebeen described in connection with what is presently considered to bepractical exemplary embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments and is intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims. Therefore, theaforementioned embodiments should be understood to be exemplary but notlimiting the present invention in any way.

What is claimed is:
 1. A positive active material composition for arechargeable lithium battery, comprising a positive active materialcoated with vanadium pentaoxide (V₂O₅), wherein the positive activematerial comprises at least one selected from lithium cobalt-basedoxide, lithium nickel cobalt manganese-based oxide and lithium nickelcobalt aluminum-based oxide; and an aqueous binder, wherein the lithiumcobalt-based oxide is Li_(a)Co_(1-b)R_(b)O₂ where R is Al or Mn(0.90≦a≦1.8 and 0<b≦0.5), the lithium nickel cobalt manganese-basedoxide is Li_(a)Ni_(1-b-c)Co_(b)Mn_(c)O_(α) (0.90≦a≦1.8, 0≦b≦0.5,0≦c≦0.05 and 0<α≦2) or Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂, and the lithiumnickel cobalt aluminum-based oxide is Li_(a)Ni_(1-b-c)Co_(b)Al_(c)O_(α)(0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and 0<α≦2).
 2. The positive activematerial composition of claim 1, wherein the vanadium pentaoxide (V₂O₅)is coated on a surface of the positive active material in a form of anisland.
 3. The positive active material composition of claim 1, whereinthe vanadium pentaoxide (V₂O₅) is included in an amount of about 0.1parts to about 5 parts by weight based on 100 parts by weight of thepositive active material.
 4. The positive active material composition ofclaim 1, wherein the vanadium pentaoxide (V₂O₅) is included in an amountof about 0.1 parts to about 1 parts by weight based on 100 parts byweight of the positive active material.
 5. The positive active materialcomposition of claim 1, wherein the positive active material coated withvanadium pentaoxide is prepared by the method comprising: mixing apositive active material, vanadium pentaoxide (V₂O₅) and an organicsolvent, agitating the mixture to evaporate an organic solvent, andheating the resultant mixture after evaporating the organic solvent toprepare a positive active material coated with vanadium pentaoxide. 6.The positive active material composition of claim 5, wherein the organicsolvent is a carbonate-based, alcohol-based, ester-based, ether-based,ketone-based, or aromatic hydrocarbon-based solvent, an aprotic solvent,or a combination thereof.
 7. The positive active material composition ofclaim 5, wherein the resultant mixture after evaporating the organicsolvent is heated in a range of from about 620° C. to about 730° C. 8.The positive active material composition of claim 1, wherein the aqueousbinder comprises at least one selected from carboxylmethylcellulose,hydroxyethylcellulose, hydroxypropylcellulose,hydroxypropylmethylcellulose, polyvinylidene fluoride,polytetrafluoroethylene, polyethylene, polypropylene, polybutadiene,polyethyleneoxide, polyvinylalcohol, polyacrylic acid and a saltthereof, polyvinylpyrrolidone, polyepichlorohydrine, polyphosphazene,polyacrylonitrile, polystyrene, polyvinylpyridine, chlorosulfonatedpolyethylene, a polyester a resin, an acrylic resin, a phenolic resin,an epoxy resin, a polymer of propylene and C2 to C8 olefin, a copolymerof (meth)acrylic acid and (meth)acrylic acid alkylester, and acombination thereof.
 9. The positive active material composition ofclaim 1, wherein the aqueous binder is included in an amount of about0.1 parts to about 10 parts by weight based on 100 parts by weight ofthe positive active material.
 10. The positive active materialcomposition of claim 1, wherein the positive active material compositionfurther comprises a conductive material.
 11. The positive activematerial composition of claim 10, wherein the conductive materialcomprises at least one selected from natural graphite, artificialgraphite, carbon black, acetylene black, ketjen black, a carbon fiber, acarbon nanotube, a metal powder, a metal fiber, and a conductivepolymer.
 12. The positive active material composition of claim 1,wherein the lithium nickel cobalt manganese-based oxide is Li_(a)Ni_(1-b-c)Co_(b)Mn_(c)O_(α) (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and 0<α≦2). 13.The positive active material composition of claim 12, wherein thelithium nickel cobalt manganese-based oxide isLi_(a)Ni_(1-b-c)Co_(b)Mn_(c)O_(α) (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and0<α≦2).
 14. The positive active material composition of claim 1, whereinthe lithium cobalt-based oxide is Li_(a)Co_(1-b)R_(b)O₂ where R is Al(0.90≦a≦1.8 and 0<b≦0.5), the lithium nickel cobalt manganese-basedoxide is Li_(a)Ni_(1-b-c)Co_(b)Mn_(c)O_(α) (0.90≦a≦1.8, 0≦b≦0.5,0≦c≦0.05 and 0<α≦2) or Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O₂, and the lithiumnickel cobalt aluminum-based oxide is Li_(a)Ni_(1-b-c)Co_(b)Al_(c)O_(α)(0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05 and 0<α≦2).